Roadway design

[jdeaneng]

I am helping a client with a roadway design. I am using AASHTO design guide to find pavement sections and my sections are coming out to be larger than they normally would be for the roads in my area. The project is an industrial park with several types of vehicles that with be using the road. My question is what is the normal loading used to represent a tractor trailer. AASHTO uses a 1.5 equivalent factor for W18 ESALs. Is there any other method or way to go about this. I believe that AASHTO is being too conservative for what i need.

 

[Ron]

It is possible that the AASHTO guide is being conservative but I doubt it. More likely is that you are underestimating the traffic loading. Industrial parks are notorious for having about every conceivable pavement loading! Further, the abrasion on the pavement surface is usually high because of the turning movements.

AASHTO design is based on Equivalent Single Axle Loads (ESAL). All loads are converted to ESAL's based on their actual loads. For example, if an axle load is 12kips not the standard 18kips, it will have an equivalence factor of less than 1. Correspondingly, if the single axle load is more than 18kips then the equivalence factor will be greater than 1. These factors are in the tables so you will have to add up all your axles and their respective ESAL to determine the appropriate structural number.

More later....

 

[oldestguy]

For highway design there is no input for what Ron mentions or the parked loaded situations. For an asphaltic concrete roadway and parking area you should check locally with the State DOT for a blend or mix that is required for high traffic in hot weather. The reason for this is that slow turning movements of loaded trucks really are rough on the asphaltic concrete mix. A very dense mix is probably what they spec.

At locations for parked trailers, as at loading docks, you should use a rigid pavement due to the concentrated loads of the dollies.

I'd also check with local municipalities as to their "standards" for industrial streets. Many times local contractors use those designs for jobs such as yours.